The invention relates to a system for the remote control of one or more jack cylinders of a hydraulically operated crane.
The jack cylinders which are associated with a hydraulically operated crane, more particularly a mobile crane, are adapted to effect hoisting, lowering, slewing, and where appropriate derricking of the jib or extension and retraction of a telescopic section of the jib. In such cranes it is advantageous if the jack cylinders can be actuated alternatively from the drivers seat or from the region of the crane base, operation from the latter region having the advantage that the operator has an adequate view of any given situation which is not normally the case in the drivers seat.
Furthermore, it is desirable, more particularly in the case of mobile cranes, to enable the jack cylinders to be remotely controlled from a position which is at a substantial distance from the crane base. Remote control of this kind becomes necessary more particualrly if the crane is to be operated by a single person.
A system for remotely controlling the jack cylinders of a hydraulic crane is known in which regulating valves have valve members, constructed as spools, which are regulated by regulating means which comprise auxiliary hydraulic cylinders. Each of the said auxiliary cylinders is biased by a separate valve the spool of which must be operated via a magnet. The entire actuating means for the regulating means of the main valves which are connected to the jack cylinders comprises a body-worn harness device which is connected to the main valves by means of hydraulic connecting ducts for remote control. Direct actuation of the actuating means is performed by means of hand levers.
The known system suffers from the disadvantage that the small hydraulic spools must be manually operated by corresponding levers against a substantial pressure in cases in which no remote control is applied. A further disadvantage of the known system is due to the fact that the operator is substantially obstructed by the body-worn harness device. This is because the said harness device is not only relatively heavy but is also connected to the crane by the hydraulic connection which comprises the connecting ducts and is therefore relatively stiff so that the mobility of the operator is noticeably restricted. A further very important disadvantage of the known system is due to the fact that the subsequent installation thereof as a simple extension of an existing hydraulic system is not possible. Instead it is necessary for practically the entire hydraulic control system to be exchanged a procedure which is exceptionally expensive, not least because of the long installation time required to this end.